[Aeris (OP)]

Antimatter. It's a thing that exists and it's something that I wanna learn more about. Just gonna jump straight into the questions this time around instead of drawing things out with a long-winded introduction.

Question 1: Why is there more matter in the universe than antimatter? Like, you can't make matter without also making an equal amount of antimatter, right? Where did it all go during the period of time right after the big bang (this is the most unreasonable questions of the bunch, so if all we have at the moment are theories/guesses as to what the actual answer may be, I'll still accept them)?
Question 2: If regular matter has a positive electric charge, and antimatter has a negative electric charge, what would matter with a neutral (or no) electric charge be called? Does such a thing even exist? CAN such a thing even exist?
Question 3: In the early stages of the universe right after the big bang, the energy density of space was high enough to support energy's spontaneous transformation into matter, and a watered-down version of this process has been replicated in particle colliders by smashing two photons (AKA carriers of electromagnetic energy) into each other to create matter and antimatter particles. Despite originating from the same place however, matter and antimatter have different properties from each other (the main one of course, being the aforenamed difference in electric charge). How can antimatter have different properties from regular matter if they were both made from the same stuff as each other?
4. Is antimatter a necessity for our universe to exist and be the way it is? Like, what does antimatter do for us that regular matter (or even dark matter) can't? How different would life be if antimatter straight up didn't exist, both in theory and in reality?           

[alancalverd]

1. Nobody knows. The assertion that you can't make one without the other is unsupported, but if equal amounts were created and not immediately separated, they would quickly annihilate. It is thus arguable that the observable universe is merely the remnant that has not yet annihilated and the complementary bits are somewhere else. 

2. "A stupidly large amount" is meaningless. A pair of 511 keV photons arising from positronium annihilation is easy to detect but  has negligible biological consequence - it's an everyday occurrence in medical imaging, and in other circumstances the reaction usually takes place inside a shielded enclosure.

3. The proposition is meaningless. We have positive, negative and zero charge particles of ordinary matter: proton, electron and neutron being the most familiar.

4. Symmetry. Your left hand does not look like your right hand but they both derive from a spherical ovum. If you start with zero charge (e.g.; two photons) you must end up with zero charge (principle of charge conservation is not violated by relativity) so whilst photon-photon interaction could produce e.g. a shower of neutrinos, it usually results in two leptons with complementary charges.

5. It is reasonable to assume (because it is tautologous) that everything that exists is a prerequisite of reality being as observed. Except for philosophers, of course, which have no discernible function.

[Halc]

Question 1: Why is there more matter in the universe than antimatter?

Unknown, but there isn't a conservation law saying that they must exist in equal quantities, but it still breaks a statistical law. Maybe some clumps of matter (galaxy clusters??) are antimatter, but somehow I think they'd be able to tell.

Questions 2: According to scientists + physicists, when matter and antimatter come into contact with each other, they annihilate each other in an instant and release a tremendous amount of energy (like, a stupidly huge amount).

But coming into contact in some classical way isn't so easy. Two opposite rocks colliding in space might release a nice bang and even some sand, but the vast majority of the material would survive and just change direction.

how was this effect even observed without the people observing it dying in the process?

It's a regular process taking place in the sun all the time for instance, and people depend on that energy. They don't die from it because they're usually not right there where it happens.

3: If regular matter has a positive electric charge, and antimatter has a negative electric charge

As Alan says, this is wrong. Both kinds of matter have both kinds of charge. Still, the pictures in the books always show a particle meeting its own antiparticle, but not stuff like a neutron meeting a positron or something.

what would matter with a neutral (or no) electric charge be called?

Neutrons and neutrinos, and their antiparticles, just to name some. Photons don't have antiparticles, but photons are not matter.

Question 4: In the early stages of the universe right after the big bang, the energy density of space was high enough to support energy's spontaneous transformation into matter, and a watered-down version of this process has been replicated in particle colliders by smashing two photons (AKA carriers of electromagnetic energy) into each other to create matter and antimatter particles

[citation needed] It's not like one can accelerate a photon. It moves at the speed of light by definition.

Is antimatter a necessity for our universe to exist and be the way it is? Like, what does antimatter do for us that regular matter (or even dark matter) can't?

As mentioned above, it is a necessary part of the metabolism of stars, enabling them to shine. That seems pretty necessary, at least to us.

How different would life be if antimatter straight up didn't exist, both in theory and in reality?

Well for starters, there'd be no us to define reality.

[Origin]

Question 2: If regular matter has a positive electric charge, and antimatter has a negative electric charge

A negatively charged electron's anti-matter particle is a positron.  A positively charged proton's anti-matter particle is a antiproton.

what would matter with a neutral (or no) electric charge be called? Does such a thing even exist? CAN such a thing even exist?

Yes, a neutron's anti-matter particle is an antineutron.

[evan_au]

How can antimatter have different properties from regular matter if they were both made from the same stuff as each other?

As mentioned above, light (photons) is its own antimatter particle.

Still unproven, one possibility is that neutrinos may be their own antiparticle - a so-called Majorana Fermion.
- Neutrinos collide with matter extremely rarely, and presumably, collide with each other less often, so it's not really possible to collide two neutrinos to see what happens.
- So when you see statements like "XYZ nuclear reaction emits an antineutrino", they implicitly mean "(if anti-neutrinos are different from neutrinos)".
See: https://en.wikipedia.org/wiki/Majorana_fermion

[Eternal Student]

Hi Aeris,
  I hope you are well.  It looks like you've got some more good questions.

  The original post seems to have been edited and some of the earlier replies don't match up well anymore.  It doesn't matter much but it might be worth asking people to look again at the OP,  or else just keep bringing your new or revised questions to the attnetion of everyone by making new posts.

   I don't have a lot of time today and it seems like you've had some good replies already.  Halc challenged you to find references in an earlier post, so let's see if we can do some of that.

Question 3: In the early stages of the universe right after the big bang, the energy density of space was high enough to support energy's spontaneous transformation into matter, and a watered-down version of this process has been replicated in particle colliders by smashing two photons (AKA carriers of electromagnetic energy) into each other to create matter and antimatter particles. Despite originating from the same place however, matter and antimatter have different properties from each other (the main one of course, being the aforenamed difference in electric charge). How can antimatter have different properties from regular matter if they were both made from the same stuff as each other?

    For the first part, it isn't actually necessary to slam two photons into each other as you described.  A single photon can change into a particle and anti-particle pair provided it is in the vicinity of a large nucleus that can take a share of what is called the recoil momentum.  This is easier to do rather than smashing two photons into each other.
    @Halc raised an issue that  direct  photon to photon collisions  haven't been done and asked for a reference or citation.  This wikipedia article does talk about the sort of thing you (Aeris) were mentioning:
https://en.wikipedia.org/wiki/Matter_creation
   However that is a low value reference.  The only high-value academic reference used in that article seems to be the following paper which I haven't read and can't comment on:
 Landau, L. D.; Lifshits, E. M. (1934). "Production of electrons and positrons by a collision of two particles". Physikalische Zeitschrift der Sowjetunion. 6: 244–257. Zbl 0010.23102.
    Anyway, I think we're willing to accept that particle and anti-particle pair production could proceed along the lines you've described.  It's sound in theory whether or not experiments involving particle colliders have actually been done.

As for the second part -
   How can antimatter have different properties from regular matter if they were both made from the same stuff as each other?
   There's probably no simple answer.  Here's one reasonable attempt:  They aren't made of the same stuff.   Just because photons can be changed into particles and anti-particles doesn't mean that these particles are made out of photons.  A particle like an electron is currently thought to be indivisible, it doesn't contain photons.  Electrons and anti-electrons are just permitted oscillations in a quantum field.  Energy in the electromagnetic field (which we would recognise as a photon) can be transferred to that electron field to create an oscillation we would recognise as an electron and an anti-electron.  However no further division of the electron or positron is possible,  if they are made out of stuff then it is electron stuff and positron stuff all the way through,  there's no photon stuff to be found in them.
    Here's a different approach (if you are determined to consider the electron as being made of "stuff").   A permananet bar magnet could theoretically be cut into little pieces, each piece turned through 180 degrees and then stuck back together again.  The final bar magnet is made of the same stuff but would now have the North and South poles reversed in orientation.  So, we can imagine a similar process of re-arranging whatever a electron is made of to obtain a particle where a negative charge has been switched to a postive charge.

Best Wishes.

[alancalverd]

Here's a different approach (if you are determined to consider the electron as being made of "stuff").   A permananet bar magnet could theoretically be cut into little pieces, each piece turned through 180 degrees and then stuck back together again.  The final bar magnet is made of the same stuff but would now have the North and South poles reversed in orientation.  So, we can imagine a similar process of re-arranging whatever a electron is made of to obtain a particle where a negative charge has been switched to a postive charge.

Beg to differ. A magnet is a dipole composed of a whole lot of dipoles. If you reverse each dipole, you reverse the magnet. The charge on an electron is spherically symmetric - a monopole - so flipping it over might reverse its angular momentum and magnetic dipole moment but won't change its charge.

If the electron were composed  of charge dipoles, they would have to be arranged radially in a sphere with their positive ends pointing inwards. So now you need to embed them in some kind of glue to stop them flying apart or spontaneously rotating, which would give the charge a half life that is not observed.

[Eternal Student]

Hi  @alancalverd

   I agree with you Alancalverd.
   It was just an analogy that I made and not a good one.   Anti-matter is an alternative solution to some equations and it has some symmetry with the corresponding matter particle.   However, there's no image or picture to go with it.

Best Wishes.   

[Eternal Student]

Hi.

   Let's look at another one of your (Aeris) questions:

4. Is antimatter a necessity for our universe to exist and be the way it is? Like, what does antimatter do for us that regular matter (or even dark matter) can't? How different would life be if antimatter straight up didn't exist, both in theory and in reality? 

    Let's take the last part of that question.   "What if antimatter didn't exist in theory?"
    Well, the Universe does seem to exist and it does seem to get on with it's usual business.  It doesn't matter whether we understand it or not.   If we were wrong about anti-matter then there's some serious flaws in the standard model of particle physics.  This will have widespread effects across much of what we thought we understood.    However, the Universe won't be affected - it works somehow and the Universe will just keep on going.   So there will be consequences in many areas of physics and many adjustments made to existing theory but that's all.
    "What if anti-matter doesn't exist in reality?"  Well, there is quite a lot of evidence for anti-matter.  We can make small quantities of anti-particles and at CERN they are experimenting with complete atoms of anti-Hydrogen.
Installed in 2000, the Antiproton Decelerator made the headlines in 2002 when large numbers of antihydrogen atoms were produced for the first time. Initial attempts were made to store antiatoms for a long enough time to be able to measure their characteristics. In 2011, an experiment announced that it had produced and trapped antihydrogen atoms for sixteen minutes, which was long enough to be able to study their properties in detail. The following year, the first measurement of the antihydrogen spectrum was published. Since 2010, the AD experiments have published numerous measurements of antimatter characteristics, comparing them to those of matter.   -Taken from https://home.cern/science/accelerators/antiproton-decelerator
   So, it seems safe to say that something like the anti-matter in the standard model of particle physics does exist.  There may be small differences between how it behaves and how it is predicted to behave - but by and large, it's anti-matter much like the stuff predicted in the models.  Indeed that's what those experiments at CERN have been focusing on.   For example, would ant-matter fall in a gravitational field just like ordinary matter (the prediction is that it would).
    "Is antimatter a necessity for our universe to exist and be the way it is?"  -  Well, yes it fits into many models of many things.  A few examples have already been mentioned in other replies.  We have used the existance and expected properties of anti-matter to develop P.E.T. scanners.  These work and have scanned numerous people in hospitals.   If anti-matter just didn't exist or didn't behave at all as we expected it to, then there's a lot of equipment and experiments that have worked but were actually just very lucky and were really explained by something else (the chances of it all working seem incredibly small).
    A similar question could be "what if the universe was mainly dominated with anti-matter instead of matter?" - well that would work based on the models we have.  There's nothing special about what we call ordinary matter, if we switched all matter for the corresponding anti-matter then it should carry on working much the same.  It's only going to be a problem if anti-matter particles are in the vicinity of it's corresponding matter particles.
    The apparent symmetry between matter and anti-matter is relevant to your (Aeris) question 1 - but I've already written enough and will be leaving that question alone for now.

Best Wishes.

[evan_au]

How different would life be if antimatter straight up didn't exist, ...in theory

So far as we know today, the universe (right down to its subatomic particles) obeys CPT symmetry.

The implication of CPT symmetry is that a "mirror-image" of our universe — with all objects having their positions reflected through an arbitrary point (corresponding to a parity inversion), all momenta reversed (corresponding to a time inversion) and with all matter replaced by antimatter (corresponding to a charge inversion) — would evolve under exactly our physical laws.

If there were no antimatter, then CPT symmetry could not exist.
- In my primitive understanding, this means subatomic collisions at LHC would have different statistics, and some Feynman diagrams would not be applicable (or would work only in one direction?).

See: https://en.wikipedia.org/wiki/CPT_symmetry#Consequences_and_implications

[Eternal Student]

Hi again.

   We seem to have lost the OP (Aeris),  which is a shame.
There was question 1 left to go.

Question 1: Why is there more matter in the universe than antimatter? Like, you can't make matter without also making an equal amount of antimatter, right? Where did it all go during the period of time right after the big bang (this is the most unreasonable questions of the bunch, so if all we have at the moment are theories/guesses as to what the actual answer may be, I'll still accept them)?

   All of your question were good but this one especially good.   Yes, it seems that when matter is created from radiation there is an equal amount of antimatter created and this is the sort of thing we might expect from the big bang.
   There are many good articles and papers asking "where did all the anti-matter go?" and there's not much point in me trying to repeat all of those here.  There's no definitive answer that I'm aware of.
   Recently, CERN seem to be obtaining some evidence for an asymmetry in the behaviour of mesons compared to their anti-mesons.  This offers some reason to suspect that there are more asymmetries to be found.   https://theconversation.com/cern-discovery-sheds-light-on-the-great-mystery-of-why-the-universe-has-less-antimatter-than-matter-147226
    Meanwhile this article  ( https://www.newscientist.com/article/dn16780-antimatter-mysteries-1-where-is-all-the-antimatter/ ) is a bit older but it's short and discusses the possibility that the anti-matter may still be there but just far away in some other part of the universe. 
   [*How far?  Possibly outside of our observable universe - although there is no theory to explain why anti-matter would have travelled that far but matter didn't do exactly the same*.]
    The second article also addresses a point that I think someone made much earlier.  If there were pockets of anti-matter in our observable universe then there should be gamma ray signals we can see where matter and anti-matter are annihilating at the border.  We haven't noticed this yet but space is big.

Best Wishes.

LATE EDITING:   * The section in [square brackets] is not implied by the New Scientist article.  See post #14 and #15.  I can't move it further away since it connects with the idea of how far away a region dominated by anti-matter instead of matter might be.

[Aeris (OP)]

@Eternal Student

I'm sorry if I haven't been as active lately. I've been quite bust with College work and getting as much sleep as possible. I also didn't really have anything to comment on here since A. All of these answers were good and understandable, and B. I don't know enough about Antimatter to discuss it further with anyone here.

[Eternal Student]

Hi @Aeris
   No worries.  I was just checking you're happy enough with the answers.
Good Luck with your college work and don't undersestimate your own ability to understand Science.  You're asking good questions and one day soon you'll be teaching it to someone else, writing for a science magazine or whatever it is you want to do.
Best Wishes.

[evan_au]

there is no theory to explain why anti-matter would have travelled that far but matter didn't do exactly the same

One such theory was that matter may have had a different gravitational attraction to itself than to antimatter. According to this theory, matter tended to clump together with other matter, and antimatter tended to clump together with other anti-matter.

The AEgIS experiment at CERN has built an anti-hydrogen factory so they can test the acceleration of antimatter (anti-Hydrogen) due to the 1g matter-gravity of Earth. Previous published results had error bars bigger than 1g, but they are making improvements and hope to measure the acceleration accurate to 1% of g.

Most physicists think the gravitational attraction of matter and anti-matter will turn out to be equal, but even a difference of 1% would hint at new physics, so it's worth doing the experiment.

https://home.cern/news/news/experiments/aegis-track-test-free-fall-antimatter

[Halc]

Halc raised an issue that direct photon to photon collisions haven't been done

I didn't say that. It's been done, and somewhat regularly. My gripe was about using particle accelerators to add energy to photons, which doesn't work.

and asked for a reference or citation.  This wikipedia article does talk about the sort of thing you (Aeris) were mentioning:
https://en.wikipedia.org/wiki/Matter_creation
   However that is a low value reference.  The only high-value academic reference used in that article seems to be the following paper which I haven't read and can't comment on

Yea, that page is pretty thin on references. The paragraph in question has no references and goes like this:

In high-energy particle colliders, matter creation events have yielded a wide variety of exotic heavy particles precipitating out of colliding photon jets (see two-photon physics).

OK, I followed the particle-collider link and it makes no mention of photons.
The two-photon link is the way to go and it says that it is done indirectly:

Two-photon physics can be studied with high-energy particle accelerators, where the accelerated particles are not the photons themselves but charged particles that will radiate photons.

So they do use particle accelerators for observation of photon-photon interactions, but they don't accelerate photons with them.

- - - -

About where the antimatter went:

Meanwhile this [newscientist] article ... discusses the possibility that the anti-matter may still be there but just far away in some other part of the universe (and possibly outside of our observable universe - although there is no theory to explain why anti-matter would have travelled that far but matter didn't do exactly the same).

Material, antimatter or otherwise, cannot interact with local matter (by separating from it say) and then 'travel' away further than the radius of the observable universe. It would have to outrun light to do that. The article made no mention of it being that far away, at least not that I saw.

The second article also addresses a point that I think someone made much earlier.  If there were pockets of anti-matter in our observable universe then there should be gamma ray signals we can see where matter and anti-matter are annihilating at the border.  We haven't noticed this yet but space is big.

This is what is being suggested I think. Say the stuff tended to clump. Early on the regions would interact and push away from each other, which results in large scale clumping into what eventually become superclusters. All the gamma rays from that interaction are hidden from us as they occur before the recombination event. So that leaves interactions today, and I don't think superclusters 'touch' each other much. Density of matter is super sparse out there (where the density of matter and antimatter would be about equal) and the collisions would be dang rare.

They said they had a satellite that would look for such signatures, waiting for launch by a shuttle mission in 2010 or 2011, but 2011 was the end of the shuttle launches, so I wonder if it got up there.

[Eternal Student]

Hi and thanks @evan_au
    It does sound a bit like something that was said earlier....

Indeed that's what those experiments at CERN have been focusing on.   For example, would antimatter fall in a gravitational field just like ordinary matter (the prediction is that it would).

    However, you've said it more eloquently and also provided references, so that's great.
Seriously, it's always good when similar things are said by different members, there's more chance it's right.  I'm also grateful for the references.

    Looks like @Halc  has just posted something....
About the particle colliders  --->  That all seems sensible.
About where the antimatter went  --->   You're right the entire section that appeared in brackets is not stated in the article.   I put it in brackets to try and separate it from the spirit of what the article said a bit - but I probably should have done more.   Anyway, there is no sensible theory to explain how or why such a thing should happen.   You're absolutely right about a light speed limit.
    Having a greater portion of anti-matter outside the observable universe requires an assumption that there is something about a region of space where inflation is still switched on that might favour anti-matter, or at least future anti-matter production.  An alternative way of phrasing this is that conditions that favour a dominance of ordinary matter could be associated with the inflaton field having had the most time to roll down to it's lowest energy.   So it's not really that anti-matter particles travelled outside the observable universe, most nucleosynthesis didn't even start until after the inflationary epoch.  Instead it's more like the precursor or values of underlying fields that will eventually cause an imbalance of anti-matter over matter - those did tend to travel beyond the observable universe and will be found in regions of space where inflation is still switched on.  This is speculation.

    You did a lot of work there Halc, chasing all those references through Wikipedia etc.  Thanks for your time, effort and insight.

Best Wishes.

LATE EDITING:  The original post has been adjusted, to further reduce the risk of anyone thinking the New Scientist article stated something that was not there.              Best Wishes.

[alancalverd]

Most physicists think the gravitational attraction of matter and anti-matter will turn out to be equal, but even a difference of 1% would hint at new physics, so it's worth doing the experiment.

It is certainly the case that electrons and positrons have the same mass, to within better than a few eV. Difficult to measure the gravitational attraction of a charged particle, however, and the damn things annihilate every time they get near a "normal" particle!

[Colin2B]

Haven’t been following this, suffering from a really bad cold.
Just skim reading so excuse me if you’ve covered this:

- Neutrinos collide with matter extremely rarely, and presumably, collide with each other less often, so it's not really possible to collide two neutrinos to see what happens.

There is a suspicion that neutrinos might be involved, but the work is slow because of their limited interactions.  Differences between oscillations of neutrinos and anti-neutrinos could point to a critical difference between matter antimatter interactions. A lot of the literature is very technical, but his article is easy to digest if you are in the middle of studies @Aeris
https://www.quantamagazine.org/neutrino-evidence-could-explain-matter-antimatter-asymmetry-20200415/

It also explains the neutrino oscillation that was discovered at Super-Kamiokande and the asymmetry between neutrinos and anti-neutrinos.

If you look up T2K you’ll find quite a bit of info, here’s some from the Sheffield team I spoke to 2 years ago when they were going over to Japan. https://www.sheffield.ac.uk/physics/research/particle/neutrino/t2k